Audio play back device when elephant crop raids

Dear all, 

As audio playback shows some results to deter elephants, we were considering using them for protecting crops (https://www.researchgate.net/publication/301708132). As most of the elephants are poached in the park, they know the Ak-47 sound and are afraid of it. The idea is to use the AK-47 shots sound combine with an elephant fear vocalisation (as the ones available on elephantlisteningproject). The advantage of this combination is that elephants should not start to be used to the sound because they are really threatened by it during their lifetime in the park. We could also other sound combination involving elephant and AK-47.

In our, Park Hyenas are also hunting young elephants so this sound could also be used alternatively.

The idea is to have these devices (number depending on the size of the crop) around crops and when the elephant is passing the edge of the crops its trigger the audio pre-recorded sound. The trigger system could be a rope cross the elephant path connected to the audio device.

The device should be battery powered or solar (but high chance of getting stolen), should be waterproof and powerfull.

In India, WRCS used a digital alarm connected to a string, but I did not find battery powered alarm system with the possibility to modify the sound displayed. (https://www.youtube.com/watch?v=7rPfFTi_Elg)

So, I would like to know if you have an idea on how to build or buy a similar system?

Thanks to all.